If you enjoy modern crime series (Sue Grafton's Kinsey Milhone books, for instance) and want to try something harder-edged, then the Travis McGee books are a great find.
Trav is an anti-hero born of the 1960s. He's rough around the edges, a womaniser like Fleming's Commander Bond, a man's man. He can be brutal and he can be appallingly chauvanist -- but he's also got a dependable moral code of his own and the guts to go through with every investigation.
This is the first book in the series so is a natural place to start (but they don't affect each other too much so it's ok if you want to begin somewhere else).
MacDonald's writing is at times bleak, others harsh, frequently contemplative. You get a pulp thriller, plenty of action, a dash of mystery and violence, combined with a pessimistic outlook on American society. There are times when MacDonald's gripes with modern life get on my nerves -- but they are more than balanced by his knife-sharp prose, engaging characters and skillful situations.
And unlike many modern novels, the Travis McGee series are all bite-size books. They're easy to read in a couple of days, not 500-page bloated behemoths. Quality -- and quantity, cos there's nearly two dozen different ones to read if you enjoy the first one.